In a tire for a heavy load such as a truck and a bus, a plurality of blocks is defined by circumferential main grooves extending in the tire circumferential direction and lug grooves, and the blocks are arranged on the whole of a tread portion so as to ensure required tire performances. However, with a tread pattern composed of the blocks, with running, a difference is caused in a wear amount between both end portions in the tire circumferential direction of the block, and heel-and-toe wear might occur in each block. This heel-and-toe wear is partial wear caused by a motion and deformation of the block during tire load rolling, in which a wear amount at a step-in end (portion contacting the ground first) of the block is smaller, while a wear amount at a kick-out end (portion contacting the ground last) is larger.
In order to cope with this problem, there is known a prior-art tire in which a block is formed into a hexagonal shape in planar view to reduce unevenness in slip in the tire circumferential direction and the tire width direction of each part in the block and a difference in the wear amount, thereby suppressing occurrence of the heel-and-toe wear (See Patent Document 1).
However, with this prior-art tire, the plurality of blocks is arranged independently in the tire width direction relatively uniformly, and there is a concern that a motion may easily occur in the block depending on the condition of use or running of the tire. Thus, securing of sufficient block rigidity and further improvement of an effect of suppressing partial wear are in demand from the viewpoint of further improvement of partial wear resistance through suppression of the motion of the block.
Moreover, in the tire having the blocks as above, the block is generally defined by arranging the lug grooves all having a certain angle and a certain width so that wet performances (traction performance and braking performance on a wet road surface, for example) are improved while an edge component is increased by the plurality of lug grooves. However, in this case, since the block rigidity tends to be lower, the partial wear resistance might be affected, and further improvement of both the wet performances and the partial wear resistance is difficult. With the prior-art tires, reduction of a noise generated during tire running is also in demand in addition to these performances.